Low detonation rate explosive compositions



United States Patent 3,252,843 LOW DETONATION RATE EXPLOSIVE COMPOSITIONS George L. Grillith, Coopersburg, William L. Schwoyer, Allentown, Thomas P. Dowling, Fullerton, and John A. Kruppenbach, Danielsville, Pa., assignors to Trojan Powder Company, a corporation of New York No Drawing. Filed Oct. 14, 1963, Ser. No. 316,115 18 Claims. (Cl. 14955) This invention relates to explosive compositions having desirably low rates of detonation which are retained over extensive and adverse periods of storage, and to a method of making the same.

The explosives art has long desired to produce explosive compositions containing conventional high explosive materials, but having very low detonation rates approaching that of black powder, which deflagrates rather than explodes at velocities in the order of 1,000 to 3,000 feet per second. Attempts to provide such explosive compositions have not been generally successful, the best formulations known to date of this kind being the so-called permissible explosives in which the particle size of ammonium nitrate, for example, is very carefully controlled to reduce the detonation rate. Generally speaking, it is known that as the particle size increases and the density of the composition correspondingly decreases, the rate of detonation will also decrease.

One of the main problems in preparing low detonation rate explosives containing coarse particles of ammonium nitrate is the fact that ammonium nitrate undergoes a number of phase changes, the most important one being around 94 F. At this temperature, the coarse particles of ammonium nitrate break down into finer particles and the result is that the density and the rate of detonation correspondingly increase. Thus, even the coarse ammonium nitrate permissible explosives do not retain low rates of detonation where a phase change occurs as described above, during storage or otherwise. 'Furthermore, the low rate of detonation of such explosives almost invariably increases appreciably when the compositions are fired confined such as in rock where they are normally used in seismic operations.

It has now been discovered that explosive compositions having low rates of detonation, in the order of 4,000 to 9,000 feet per second, can be formulated with ammonium nitrate or nitrate-based explosive components and that such compositions retain these desired rates of detonation consistently over extended periods of storage. More specifically, it has been found that if ammonium nitrate or nitrate-based explosive components are used in relatively fine particle sizes so as to prevent further breakdown during phase changes, and that if such compositions are modified by inclusion of an inorganic density-reducing agent which does not take part in the explosive reactions,

the low rates of detonation which such compositions possess initially can be retained throughout the life of the compositions. Furthermore, the compositions of the invention can be detonated confined or unconfined with a relatively consistent low rate of detonation and any small differences between the confined and unconfined detonation rates can be easily taken into account beforehand in formulating or packaging a specific composition. The explosive compositions of the invention thus satisfy the previously-mentioned need in the art and offer many advantages in commercial operations.

First of all, once packaged in containers in a constant weight per container, the rate of detonation of any particular explosive composition will not change greatly over a long storage period. Secondly, since the inorganic density-reducing materials do not take part in the explosive reactions, they do not affect the energy or power deice veloped upon detonation, so that their presence need not be accounted for from the energy standpoint in formulating specific compositions with specific detonation rates. The compositions can be safely packaged directly into cans with conventional loading and packaging equipment and a particularly valuable feature is the fact that the explosive compositions are insensitive to detonation by a commercial blasting cap and can be stored and shipped under government regulations as nitro-carbonitrate compositions. Furthermore, packaged explosive compositions of the invention having different rates of detonation can be assembled or loaded with each other for firing in various ratios to obtain intermediate rates of detonation in a reliable and consistent manner. The compositions of the invention are of particular utility in seismic operations, but they have a wide range of applications as will be evident to those skilled in the art.

The explosive compositions of the invention contain inorganic nitrates preferably as the principal explosive components. Such components may comprise ammonium nitrate alone or ammonium nitrate in mixture with inorganic metal nitrates such as alkali metal and/or alkaline earth metal nitrates. Where the ammonium nitrate'is used in mixture with other metal nitrates, the ammonium nitrate should constitute at least about 50% of the weight of the mixture. As previously noted, the particle size of the nitrate explosive components should be relatively fine in order to prevent a change in the low rates of detonation desired because of phase changes. Generally speaking, substantially all particles of the nitrate explosive components should pass through a #15 screen, US. Standard Series and preferably the particles are used in a slightly finer size so that substantially all of the particles pass through a #20 screen. Particularly good results have been achieved by crushing and grinding dense ammonium nitrate prills containing appreciable quantities, up to about 2% by weight, of magnesium or calcium nitrates, the crushed particles substantially all passing through #15 screen. Such magnesium and/or calcium nitrate-containing prills are disclosed in US. Patent 3,030,179, and while the prills as such are too insensitive to detonation to be used in the compositions of this invention, the finer nitrate particles obtained by' crushing the prills to the above-mentioned particle sizes can be used with excellent results. The quantity of nitrate explosive components used in the explosive compositions of the invention may vary from about 30% to about of the total weight of the composition.

In accordance with the invention, an inorganic densityreducing agent is included in the explosive composition in amounts varying from about 10% to about 25 by weight of the total composition. Such inorganic agents may generally consist of any metal oxide which is in a stable oxidation state, so that the oxide will not take part in the reactions developed on detonation of the composition. While a single metal oxide may be usedalone, better results will be achieved with mixtures of metal oxides and, in this connection, of particular utility are certain naturally occurring mixtures of metal oxides. For example, vermiculite, a naturally found mixture of about 39% SiO 21% MgO, 15% A1 0 9% Fe O 1% CaO and 59% H O, can be used. Other examples are perlite, a glassy rock similar to obsidian and containing 65-75% SiO 1020% A1 0 25% H 0 and smaller amounts of soda, potash and lime. The highly-porous igneous rock pumice, 'which contains 67-75% SiO and 1020% A1 0 may also be used. Asbestos and the zeolites, the latter being naturally occurring hydrated sodium silicoaluminates and sodium calcium silico-aluminates, may also be employed.

In using the metal oxide or mixtures thereof, it is important that the particle size be relatively coarse as compared to the very fine particles of these materials which are conventionally used for coating pruposes. Thus, for the purposes of this invention, the particle size of the metal oxide should be such that substantially all of the particles are retained upon a #150 screen, U.S. Standard Series, and preferably a #120 screen.

While it is of critical importance to include the inorganic agents described above in the explosive compositions of the invention, it is also possible to include limited quantities of carbonaceous, density-reducing agents. Such carbonaceous agents, for example, bagasse, saw dust, and nut meals, are not as desirable since, first of all, they take part in the explosive reactions and generate toxic carbon monoxide and dioxide. Secondly, they tend to increase the rate of detonation of the explosive composition should the composition beocme compacted. Therefore, such carbonaceous density reducing agents, if used, should not be present in amounts greater than the amount of the inorganic noncarbonaceous agents previously described. Thus, for purposes of oxygen balance or other considerations apart from the density of the explosive compositions, carbonaceous density reducing agents may be used, but only in the limited quantities specified wherein the weight of the carbonaceous agent does not exceed the weight of the inorganic noncarbonaceous agent.

The explosive compositions of the invention require a sensitizer in amounts varying from about 3% to 30% by weight of the total composition. These sensitizers may be various conventional detonable organic compounds such as nitrostarch, nitnoglycerine, trinitrotoluene and other nitrotoluenes, nitronaphthalene, trimethylolethane trinitrate, pentaerythritol tetranitrate, pentolites (mixtures of pentaerythritol tetranitrate and dinitrotoluene) and cylcodinitrotrimethylenetetramine.

Particularly good results have been achieved with use of dinitrotoluene oil as the organic sensitizer. This material comprises a dinitrotoluene having a low melting point so as to be in the form of an oily liquid, but solid dinitrotoluenes or solid-liquid mixtures may be used as well. The explosive compositions of the invention may contain conventional explosive ingredients in addition to the nitrate explosive components and sensitizers described above, as the inorganic density-reducing agents will provide the advantages of not taking part in the explosive reactions and not causing changes in the detonation rate in widely differing formulations. For example, compositions containing mixtures of nitrate explosive components wherein the weight of ammonium nitrate is less than half the total weight of the nitrate mixture, or compositions based solely on other conventional explosive components without any nitrates, may be greatly improved by addition of the inorganic density reducing agents and therefore are within the scope of the invention.

The explosive compositions of the invention can be prepared in conventional mixing equipment and safely packaged into cans of the type disclosed in U.S. Patent No. 3,013,092. The packages should be filled to a constant weight package and the desirable low rates of detonation possessed by the explosive compositions of the invention will not thereafter change substantially, particularly where only the inorganic density reducing agent is included.

Further details of the invention will be illustrated in the following examples which represent preferred embodiments thereof. All proportions given in the examples are by weight unless otherwise indicated.

Example I A series of explosive compositions were prepared in accordance with the following table, and each of the compositions was packed in a 2 inch by 6 inch can with conventional equipment, the cans detonated and the rates of detonation recorded. fined under 3 feet of water.

The cans were fired con- As will be noted, composition #1, representing the basic formulation of ammonium nitrate and organic sensitizer, had a relatively high rate of detonation, 10,900 feet per second. Adding sodium chloride to cool the explosive reactions, the rate of detonation did not change significantly, decreasing slightly to 10,400 feet per second (Composition #2). 15% of pecan meal added in composition #3 did reduce the rate of detonation to 7,250 feet per second but, as previously pointed out, carbonaceous agents are objectionable because they take part in the explosive reactions and also give rise to an increase in detonation rates upon compaction. As will be seen, when 15 of vermiculite was replaced for the 15% of pecan meal, the rate of detonation decreased almost twice as much to 4,300 feet per second. Furthermore, when the sodium chloride was deleted in composition #5, the vermiculite was still eifective for maintaining the rate of detonation below the detonation rate of the composition containing the pecan meal.

Over extended periods of storage at temperatures above and below 94 F., the rates of detonation of compositions 4 and 5 remained substantially at the low values reported in the foregoing table.

Example 2 In this example, a series of explosive compositions were prepared, packed in 2 inch by 6 inch cans by conventional loading equipment to a gross weight of 335 grams, detonated confined under 3 feet of water and the rate of detonation recorded as in the following table:

Explosive Compositions Ingredients Ammonium Nitrate (crushed prills) Dinitrotoluene oiL- Rate of Detonation ft./sec 5,

examples had the following screen analysis according to the U.S. Standard Series:

Percent On Screen-18 1 On Screen-35 14 On Screen-60 34 On Screen-80 12 On Screen-420 12 On Screen230 12 Thru Screen-230 15 It will be understood that it is intended to cover all changes and modifications of the preferred form of structure herein chosen for the purpose of illustration which do not constitute departures from the spirit and scope of the invention.

The following is claimed:

1. An explosive composition having a stable low rate of detonation which comprises inorganic nitrate explosive components substantially all the particles of which pass #15 screen, U.S. Standard Series, in admixture with at least one metal oxide substantially all the particles of which are retained upon a #150 screen, U.S. Standard Series, said composition having a rate of detonation up to about 9,000 feet per second.

2. An explosive composition having a stable low rate of detonation which comprises nitrate explosive components selected from the group consisting of ammonium nitrate and ammonium nitrate in mixture with inorganic metal nitrate, at least about half the weight of said com ponents being ammonium nitrate and substantially all the particles of said components passing #15 screen, U.S. Standard Series, at least one inorganic metal oxide substantially all the particles of which are retained upon #150 screen, U.S. Standard Series, and a sensitizer for said nitrate explosive components, said composition having a rate of detonation up to about 9,000 feet per second.

3. An explosive composition as in claim 2 which includes finely-divided carbonaceous particles in an amount not in excess of that of said metal oxide.

4. An explosive composition as in claim 2 wherein said metal oxide is vermiculite oxides.

5. An explosive composition as in claim 2 wherein said metal oxide is perlite oxides.

6. An explosive composition as in claim 2 wherein said metal oxide is pumice oxides.

7. An explosive composition having a stable low rate of detonation which comprises from about 30% to about 80% by weight of nitrate explosive components selected from the group consisting of ammonium nitrate and ammonium nitrate in mixture with inorganic metal nitrate, at least about half the weight of said components being ammonium nitrate and substantially all the particles of said components passing #15 screen, U.S. Standard Series, from about to about 25% by weight of at least one inorganic metal oxide substantially all the particles of which are retained by #150 screen, U.S. Standard Series, and from about 3% to about 30% by weight of a sensitizer for said nitrate explosive components, all of the foregoing percentages being based on the weight of the total composition and said composition having a rate of detonation up to about 9,000 feet per second.

8. An explosive composition as in claim 7 wherein said explosive components are solely ammonium nitrate.

9. An explosive composition as in claim 7 wherein said metal oxide is vermiculite oxides.

10. An explosive composition as in claim 7 wherein said metal oxide is perlite solids.

11. An explosive composition as in claim 7 wherein said sensitizer is a detonable organic compound.

12. An explosive composition as in claim 7 wherein said sensitizer is dinitrotoluene.

13. An explosive composition as in claim 7 wherein said explosive components are crushed particles derived from hard, dense prills containing ammonium nitrate and alkaline earth metal nitrate.

14. The method of forming an explosive composition having a low rate of detonation which comprises mixing together from about 30% to about of nitrate ex plosive components selected from the group consisting of ammonium nitrate and ammonium nitrate in mixture with inorganic metal nitrate, at least half of the weight of said components being ammonium nitrate and substantially all the particles of said components passing #15 screen, U.S. Standard Series, from about 10% to about 25% of at least one metal oxide substantially all the particles of which are retained upon #150 screen, U.S. Standard Series, and a sensitizer for said nitrate explosive components, all of the foregoing percentages being based on the total weight of the composition and said composition having a rate of detonation up toabout 9,000 feet per second.

15. The method as in claim 14, wherein said metal oxide is vermiculite oxides.

16. The method as in claim 14 wherein said metal oxide is perlite oxides.

17. The method as in claim 14 wherein said sensitizer is dinitrotoluene.

18. An explosive composition having a stable low rate of detonation which comprises nitrate explosive components selected from the group consisting of ammonium nitrate and ammonium nitrate in mixture with inorganic metal nitrate, substantially all the particles of said components passing #20 screen, U.S. Standard Series, from about 10% to about 25 of at least one inorganic metal oxide based on the weight of the total composition, substantially all the particles of the metal oxide being retained upon a screen, U.S. Standard Series, and a sensitizer for said nitrate explosive components, said composition having a rate of detonation up to about 9,000 feet per second.

References Cited by the Examiner UNITED STATES PATENTS 1,881,307 10/1932 Bashford l4946 2,589,532 3/1952 Byers l4939 2,754,755 7/1956 Ruth et al. l4939 X 2,932,610 2/1960 Harper et al. 149-46 3,164,503 1/1965 Gehrig l4918 REUBEN EPSTEIN, Primary Examiner. BENJAMIN R. PADGETT, Examiner A. G. BOWEN, Assistant Examiner. 

1. AN EXPLOSIVE COMPOSITION HAVING A STABLE LOW RATE OF DETONATION WHICH COMPRISES INORGANIC NITRATE EXPLOSIVE COMPONENTS SUBSTANTIALLY ALL THE PARTICLES OF WHICH PASS #15 SCREEN, U.S. STANDARD SERIES, IN ADMIXTURE WITH AT LEAST ONE METAL OXIDE SUBSTANTIALLY ALL THE PARTICLES OF WHICH ARE RETAINED UPON A #150 SCREEN, U.S. STANDARD SERIES, SAID COMPOSITION HAVING A RATE OF DETONATION UP TO ABOUT 9,000 FEET PER SECOND. 